Fixation of optical brightening agents onto papermaking fiber

ABSTRACT

The present invention relates to a method of increasing the brightness of pulp, pulp made from such methods and methods of using such pulp.

This application claims the benefit of U.S. provisional application Ser.No. 60/654,712, filed Feb. 19, 2005, and claims priority from U.S.application Ser. No. ______, filed Feb. 21, 2006, and entitled “PULP ANDPAPER HAVING INCREASED BRIGHTNESS”, which are hereby incorporated, intheir entirety, herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method of increasing the brightnessof pulp, pulp made from such methods and methods of using such pulp.

BACKGROUND OF THE INVENTION

Bleaching is a common method for increasing the whiteness of pulp.Industry practice for improving appearance of fluff pulp is to bleachthe pulp to ever-higher levels of brightness (the Technical Associationof the Pulp & Paper Industry (“TAPPI”) or the International Organizationfor Standardization (“ISO”)). However, bleaching is expensive,environmentally harsh and often is a source of manufacturing bottleneck.Widespread consumer preference for a brighter, whiter pulp drivesmanufacturers to pursue ever more aggressive bleaching strategies. Whilehighly bleached pulps are “whiter” than their less-bleached cousins,they are still yellow-white in color. A yellow-white product isundesirable. Countless studies suggest that consumers clearly favor ablue-white over a yellow-white color. The former is perceived to bewhiter, i.e., “fresh”, “new” and “clean”, while the latter is judged tobe “old”, “faded”, and “dirty”.

While bleaching directly elevates brightness, it only indirectlyelevates whiteness. Due to the latter, bleaching is not always the mostefficient method for boosting product whiteness. For example, even afteraggressive bleaching, a product's whiteness can always be extendedbeyond that achievable with bleaching alone by judicious addition ofcolorant.

The practice of pre-coloring papermaking pulp is not usually done nor isit necessarily desired. With the former, intentional alteration ofoptical properties often ends up degrading product specifications suchas TAPPI brightness, which is undesirable. With the latter, one runs therisk that colorants may not survive the unpredictable manufacturingenvironments of downstream processes. This is because previously appliedcolorant can be adversely affected chemically and/or physically duringpost-processing operations resulting in unexpected or undesirable colorchanges or even full loss of color. Furthermore, some colorants can belost or rendered ineffective during various post-processing operationsdisrupting process health and reliability. Therefore, any opticalenhancement is usually accomplished by addition of tinting colorants,fillers, and/or fluorescent dye during the papermaking stage. A processfor enhancing the whiteness, brightness, and chromaticity of papermakingfibers has been described in U.S. Pat. No. 5,482,514. The processrelates to adding photoactivators, particularly water-solublephthalocyanines, to papermaking fibers to enhance their opticalproperties by a catalytic photosensitizer bleaching process. Theresulting bleached papermaking fibers can be advantageously incorporatedinto paper sheets.

With fluff pulp, as well as most pulp and paper products, TAPPIbrightness serves as the de facto standard in lieu of anindustry-specific whiteness specification such as CIE Whiteness(Commission Internationale d'Eclairage). Because of this, brightnessserves two key roles. First, brightness is a manufacturing parameter.Second, brightness is a specification for classifying finished productgrades. The implicit, but dubious, assumption to this day has been thatbrightness is equivalent to whiteness. Common papermaking practice is toeither add blue tinting dyes or tinting pigments and/or different typesof blue-violet fluorescent dyes to boost whiteness properties. Tintingcolorants are either finely ground colored pigments suspended in adispersant or synthetically produced direct dyes. Tinting dyes have someaffinity to cellulose while tinting pigments have little to none.

Fluorescent whitening agents (FWA) or optical brightening agents (OBA)are used in the pulp and paper industry are of three types: di-, tetra-,or hexasulphonated stilbene compounds, for example. These chemicalsrequire ultraviolet (UV) light to excite fluorescence. While there isstrong UV content in daylight, even common office lights produce enoughUV light to permit some excitation. During papermaking, OBAs are addedat the wet end of papermaking processes, which include for example, themachine chest and/or the fan pump, where the fiber solution is at lowconsistencies that are less than about 3% solids. At these conventionaladdition points, much OBA is lost to waste as the OBA does notnecessarily have a strong affinity to the fibers in solution.Accordingly, the OBA must be added at high concentrations (lbs/ton offiber or pulp) in order to achieve high quality fibers having highbrightness and high brightness improvements.

Accordingly, there exists a need for a pulp having improved whitenessand brightness. A need also exists for a method for makingwhitened/brightened pulp for any use, especially papermaking and fluffpulp, while using less OBA to obtain such levels of whiteness andbrightness at less cost. The present invention seeks to fulfill theseneeds and provides further related advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Graphs of ISO Brightness v.s OBA Level of Handsheets made frompulp treated with OBA, full data set.

FIG. 2: Graphs of ISO Brightness v.s OBA Level of Handsheets made frompulp treated with OBA, dose data set.

FIG. 3: Graphs of ISO Brightness v.s OBA Level of Handsheets made frompulp treated with OBA, effect of OBA dose in the presence of 10 and 20%filler.

FIG. 4: Graphs of ISO Brightness v.s OBA Level of Handsheets made frompulp treated with OBA effect of OBA dose in the presence of 10 and 20%filler, regression lines added.

FIG. 5: Raman spectra of OBA only and pulp with different levels of OBAadded conventionally.

FIG. 6: Raman spectra of pulp with different levels of OBA addedaccording to one aspect of the present invention.

FIG. 7: Raman spectra of pulp with different levels of OBA addedconventionally and added according to one aspect of the presentinvention.

FIG. 8: Graph of the peak ratio (1604/900 cm⁻¹) within Raman spectra ofpulp with different levels of OBA added conventionally and addedaccording to one aspect of the present invention (Hardwood and Softwood)as depicted in Table 10.

FIG. 9: UV/VIS absorbance at 350 nm of water estract vs. Actual Amountof OBA on fibers, lbs/ton.

FIG. 10: OBA peak height vs. OBA added (lbs/ton) via the conventionaladdition method and added according to one aspect of the presentinvention (Hardwood and Softwood).

FIG. 11: OBA peak height vs. OBA added (lbs/ton) via the conventionaladdition method and added according to one aspect of the presentinvention (Hardwood and Softwood).

DETAILED DESCRIPTION OF THE INVENTION

The present inventor has surprisingly found an method of efficientlyincreasing the brightness and whiteness of pulp and paper while usingless OBA applied thereto, thereby providing for a much more efficientmanner of providing a fiber-OBA complex containing greater fiber-OBAinteraction on the whole than conventional methodologies of creating afiber-OBA complex. Such a fiber-OBA complex made by the method accordingto the present invention has greater increases in brightness andwhiteness than the fiber alone as compared to traditional methodologiesas described below.

The present invention relates, in part, to a method of making pulp. Thepulp may be fluff or papermaking pulp. The method may be used and addedto any traditional methods of making papermaking or fluff pulp. The pulpmay be used in any conventional uses of pulp, including any conventionalpapermaking processes of making paper and/or paperboard substrates. Suchconventional pulp and papermaking processes in the pulp, paper andpaperboard art may be found, for example, in “Handbook For Pulp & PaperTechnologies”, 2^(nd) Edition, G. A. Smook, Angus Wilde Publications(1992) and references cited therein, which are hereby incorporated, intheir entirety, herein by reference.

A typical pulp/paper making process may include, but is not limited to,the following stages:

A. Digesting stage where wood chips are digested to release pulp fibersfrom the lignin;

B. Brownstock Washing Stage where the pulp from the Digesting Stage iswashed;

C. Bleaching/Extraction Stages where the pulp is extracted with andbleached with various chemicals such as oxygen in oxygendelignification, chlorine dioxide, elemental chlorine, peroxide, ozone,and the like followed by one or more washing stages;

D. High Density Storage Stage where the bleached/washed pulp is storedat relatively high density as for example more than about 7%, preferablyfrom about 7.5 to about 15%, and preferably from about 10 to about 12%;

E. Low Density Storage Stage where the bleached/washed pulp is stored atrelatively low density as for example equal to or less than about 7%,preferably from about 3% to 7%, and more preferably from about 10 toabout 12%;

D. Pulp Refining Stage where the pulp is refined at a consistencypreferably of from about 4 to about 5%;

E. Blend Chest/Machine Chest Stages where the pulp having a consistencypreferably from about 3 to about 4% is mixed with wet end chemicals usedin paper making such as fillers, retention aids, dyes and opticalbrighteners and the like. Such a traditional processes may includerepeats of any one or more of the above-mentioned steps. In addition,the present invention may be combined with traditional methods of addingOBA to fibers, such as the conventional wet-end addition points as wellas size press addition points and coating addition points, when makingpaper and/or paperboard.

The present invention relates, in part, to a method of adding OBA tofibers at any point after the last bleaching/extraction stage and up toand prior to the Blend Chest/Machine Chest Stages.

The source of the fibers may be from any fibrous plant. The papersubstrate of the present invention may contain recycled fibers, deinkedfibers and/or virgin fibers. Examples of such fibrous plants are trees,including hardwood and softwood fibrous trees, including mixturesthereof. In certain embodiments, at least a portion of the pulp fibersmay be provided from non-woody herbaceous plants including, but notlimited to, kenaf, hemp, jute, flax, sisal, or abaca although legalrestrictions and other considerations may make the utilization of hempand other fiber sources impractical or impossible. Either bleached orunbleached pulp fiber may be utilized in the process of this invention.Recycled pulp fibers are also suitable for use.

The pulp of the present invention may contain from 1 to 99 wt %,preferably from 5 to 95 wt %, cellulose fibers originating from hardwoodspecies and/or softwood species based upon the total amount of cellulosefibers. This range includes 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, 80, 85, 90, 95, and 100wt %, including any and allranges and subranges therein, based upon the total amount of cellulosefibers.

When the pulp may contain both hardwood and softwood fibers, it ispreferable that the hardwood/softwood ratio be from 0.001 to 1000. Thisrange may include 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5,1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 includingany and all ranges and subranges therein and well as any ranges andsubranges therein the inverse of such ratios.

Optical brighteners are dye-like fluorescent compounds which absorb theshort-wave ultraviolet light not visible to the human eye and emit it aslonger-wave blue light, with the result that the human eye perceives ahigher degree of whiteness and the degree of whiteness is thusincreased. The optical brighteners used in the paper industry aregenerally 1,3,5-triazinyl derivatives of4,4′-diaminostilbene-2,2′-disulfonic acid, which may carry additionalsulfo groups, for example altogether 2, 4 or 6. An overview of suchbrighteners is to be found, for example, in Ullmann's Encyclopedia ofIndustrial Chemistry, Sixth Edition, 2000 Electronic Release, OPTICALBRIGHTENERS—Chemistry of Technical Products. However, recent brightenertypes are also suitable, for example derivatives of4,4′-distyrylbiphenyl, as likewise described in the abovementionedUllmann's Encyclopedia of Industrial Chemistry, which is herebyincorporated, in its entirety, herein by reference. While the presentinvention prefers methods and fiber-OBA complexes using theabove-mentioned OBA, the present invention is in no way limited to suchexemplified embodiments and any OBA may be utilized.

The present invention relates in part, to a fiber:OBA complex in whichthe affinity of the OBA added to the fiber according to presentinvention is preferably greater than that when the OBA is added to thefiber conventionally. When the OBA is added to the fiber according tothe method of the present invention, there is 30 to 60% reduction in theOBA required to be added than that of conventional methods and additionpoints. The reduction may be 30, 31, 32, 33, 34, 35, 40, 45, 50, 55, 56,57, 58, 59, and 60% compared to that required in conventional methodsand addition points, including any and all ranges and subranges therein.

The increased affinity of the OBA to the fiber may be measured byextraction methods using any solvent, preferably water, at anytemperature. Because the OBA has increased affinity to the fiber overallin the present inventive pulps and paper substrates made therefromcompared to conventional pulp, it will take a longer period of time forthe OBA to be extracted from the pulp:OBA complex of the presentinvention (pulp and/or paper) at a given time period and temperature fora given solvent.

In addition, the present invention preferably relates to a method ofincreasing the penetration of OBA into the cell wall of a fiber.Preferably, there is a greater amount of OBA that has penetrated thecell wall of a fiber treated according to the present invention thanthat of fibers treated by conventional methods. More preferably, theamount of OBA present within the cell wall of the fiber is increased byat least 1% than the amount of OBA present within the cell wall of fiberthat was treated in conventional methods. However, it is more preferredthat the amount of OBA present within the cell wall of the fiber isincreased by at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100, 200, 300, 500, and1000% than the amount of OBA present within the cell wall of fiber thatwas treated in conventional methods, including any and all ranges andsubranges therein.

The amount of OBA present within the cell wall of fiber may be measured,for example, by microscopy, more specifically fluorescent microscopy.

While any amount of OBA may be added to the fiber so long as it is addedat any point after the last bleaching/extraction stage and up to andprior to the Blend Chest/Machine Chest Stages, it is preferable thatfrom 1 to 60 lbs of OBA per ton of fiber, more preferably not more then30 lbs/ton, most preferably, not more than 15 lbs/ton OBA/fiber. Thisrange includes 60, 55, 50, 45, 40, 30, 35, 30, 25, 20, 15, 14, 13, 12,11, 10, 9, 8, 7, 6, 5, 4, 3, 2, and 1 lbs of OBA per ton of fiber(lbs/ton) including any and all ranges and subranges therein.

In addition, the fiber may be in solution, or added to solution at thesame time, as the OBA. Preferably, the fiber is in solution prior tocontacting the OBA thereto. In one embodiment of the present invention,the fiber may have any consistency. However, it is preferably to have aconsistency that is equal to or greater than 4% solids, more preferably,not less than about 5 % solids, most preferably, not less than about 10%solids. In addition, it is preferable that the fibers have a consistencythat is not more than about 35% solids, preferably not more than 20%solids, more preferably not more than about 15% solids. These rangesinclude 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,and 20% solids as the fiber consistency at the time the OBA is addedthereto, including any and all ranges and subranges therein.

At the time of the addition of the OBA to the fiber, the pH may be anypH. Preferably, the pH may range from 2.5 to 8.0, more preferably from3.5 to 5.5. This range includes 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0,6.5, 7.0, 7.5, and 8.0, including any and all ranges and subrangestherein.

At the time of the addition of the OBA to the fiber, the temperature maybe any temperature. However, it is preferable that means be applied,such as heating, so as to generate a temperature that is from 35 to 95°C., preferably from 50 to 90° C., more preferably from 60 to 80° C. Thisrange includes 35, 40, 45, 50, 55, 60, 61, 62, 63, 64, 65, 66, 67, 68,69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 85, 90 and 95° C.,including any and all ranges and subranges therein.

The time in which the OBA is contacted with the fiber may be for anyduration of time. Preferably, the OBA and fiber may be contacted from 30minutes to 12 hours, more preferably from 45 minutes to 8 hours, mostpreferably from 1 hour to 6 hours. This range includes 0.5, 0.75, 1,1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5,4.75, 5, 5.25, 5.5, 5.75, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11, and 12hrs, including any and all ranges and subranges therein.

At the time of contacting the OBA with the fiber, retention aids mayoptionally be present or added therewith. Alum and/or cationic retentionaids are examples of such retention aids. Examples of retention aids isfound in U.S. Provisional Patent Application 60/660703, filed Mar. 11,2005, and U.S. Pat. No. 6,379,497, which are hereby incorporated, intheir entirety, herein by reference. However, any retention aid commonlyused with OBAs may be used. While the retention aid may be present inany amount, or not at all, preferably, the amount of retention aidpresent is less than that required during conventional processes andaddition points used to contact OBA with fibers. Most preferably, noretention aids are used. If retention aids are used, it is preferablethat there is at least a 1% reduction in the amount of retention aidpresent as compared to that of conventional methods and addition pointsfor contacting OBA with fiber. The preferred reduction is at least 2, 3,4, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 75, 100, 200, 300, 500, and1000% reduction in the amount of retention aid present in the presentinvention as compared to conventional methods and addition points forcontacting OBA with fiber, including any and all ranges and sub-rangestherein.

While the fiber may be refined at any time, preferably, the fiber isrefined after the OBA is contacted with the fiber. Therefore, thefiber:OBA complex of the present invention is refined. Accordingly, anyconventional refining may occur, including but not limited the chemicalrefining, mechanical refining, thermochemical refining, thermomechanicalrefining, chemithermomechanical refining, etc may occur. Therefore thepulp produced may include TMP, CTMP, MP, BCTMP, etc.

The pulp of the present invention and method of making the same may beincorporated into any traditional papermaking process. The pulp and/orpaper substrate may also include other conventional additives such as,for example, starch, mineral and polymeric fillers, sizing agents,retention aids, and strengthening polymers. Among the fillers that maybe used are organic and inorganic pigments such as, by way of example,minerals such as calcium carbonate, kaolin, and talc and expanded andexpandable microspheres. Other conventional additives include, but arenot restricted to, wet strength resins, internal sizes, dry strengthresins, alum, fillers, pigments and dyes. Dyes that are especiallypreferably are those of the blue dye type which are capable ofincreasing the CIE Whiteness of the pulp and/or paper substrate.Preferably, pulp and paper substrate of the present invention madeaccording to the present invention is capable of achieving CIE Whitenessthat is much higher than conventional pulps and substrates made byconventional methods, even at CIE Whiteness levels that usually resultin decreased ISO brightness levels.

The pulp and/or paper substrate of the present invention may have anyCIE whiteness, but preferably has a CIE whiteness of greater than 70,more preferably greater than 100, most preferably greater than 125 oreven greater than 150. The CIE whiteness may be in the range of from 125to 200, preferably from 130 to 200, most preferably from 150 to 200. TheCIE whiteness range may be greater than or equal to 70, 80, 90, 100,110, 120, 125, 130, 135, 140, 145, 150, 155, 160,65, 170, 175, 180, 185,190, 195, and 200 CIE whiteness points, including any and all ranges andsubranges therein. Examples of measuring CIE whiteness and obtainingsuch whiteness in a fiber and paper made therefrom can be found, forexample, in U.S. Pat. No. 6,893,473, which is hereby incorporated, inits entirety, herein by reference.

Preferably, the pulp and/or paper substrate of the present invention hasa CIE whiteness that is increased over conventional pulp and/or papersubstrates made by conventional methods. The preferred increase is atleast 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 75, 100, 200, 300,500, and 1000% increase in CIE whiteness as compared to that ofconventional pulps, paper substrates made by conventional methods andaddition points for contacting OBA with fiber, including any and allranges and sub-ranges therein.

The pulp and paper substrate of the present invention may have any ISObrightness, but preferably greater than 80, more preferably greater than90, most preferably greater than 95 ISO brightness points. The ISObrightness may be preferably from 80 to 100, more preferably from 90 to100, most preferably from 95 to 100 ISO brightness points. This rangeinclude greater than or equal to 80, 85, 90, 91, 92, 93, 94, 95, 96, 97,98, 99, and 100 ISO brightness points, including any and all ranges andsubranges therein. Examples of measuring ISO brightness and obtainingsuch brightness in a papermaking fiber and paper made therefrom can befound, for example, in U.S. Pat. No. 6,893,473, which is herebyincorporated, in its entirety, herein by reference.

Preferably, the pulp and/or paper substrate of the present invention hasan ISO brightness that is increased over conventional pulp and/or papersubstrates made by conventional methods. The preferred increase is atleast 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 75, 100, 200, 300,500, and 1000% increase in an ISO brightness as compared to that ofconventional pulps, paper substrates made by conventional methods andaddition points for contacting OBA with fiber, including any and allranges and sub-ranges therein.

The present invention is explained in more detail with the aid of thefollowing embodiment example which is not intended to limit the scope ofthe present invention in any manner.

EXAMPLES Comparative Example 1

Lab experiments were carried out to simulate a commercial paper makingoperation, in which T-100, a Clariant's tetrasulphonated OBA product,was added into three bleached hardwood Kraft pulp samples. A low speedlab Warring blender was used for mixing pulp with all chemicals. Priorto the optical brightener (“OBA”) addition, deionized water was addedinto the 5 gm oven dry pulp sample to reduce its consistency to 1%consistency. Shortly after the OBA addition, 5 ml of 5% alum solution ofalum was added into the pulp mixture to complete the attachment of allOBA onto the fiber. After one minute mixing in the blender, the pulpmixture was dewatered to form a brightness pad, following the standardTappi pulp brightness testing procedure. Three pulp samples and threedosage of T-100 were used in these experiments. Brightness results onindividual pulp samples, before and after OBA fixation, are as follows:TABLE 1 Hardwood #1 Hardwood #2 Hardwood #3 Brightness Brite BrightnessBrite Brightness Brite (GE) Gain (GE) Gain (GE) Gain 0 80.5 0 84.4 086.6 0 4 83.1 2.6 87.7 3.3 90.0 3.5 8 84.2 3.7 89.7 5.1 90.4 3.8 16 84.94.3 89.4 5.0 90.7 4.1

Comparative Example 2

Lab experiments were carried out to simulate a commercial paper makingoperation in which T-100, a Clariant's tetrasulphonated OBA product, wasadded into one southern hardwood Kraft pulp sample. A low speed labWarring blender was used for mixing pulp with all chemicals. Prior tothe OBA addition, deionized water was added into the 5 gm oven dry pulpsample to reduce its consistency to 1% consistency. For experiments inseries I, shortly after the OBA addition, 5 ml of 5% alum solution ofalum was added into the pulp mixture to complete the attachment of allOBA onto the fiber. No alum was used for experiments in series II. Forboth cases, after one minute mixing in the blender, the pulp mixture wasdewatered to form a brightness pad, following the standard Tappi pulpbrightness testing procedure. Three pulp samples and three dosage ofT-100 were used in these experiments. Brightness results on individualpulp samples, before and after OBA fixation, are as follows: TABLE 2Series I - No Alum Series II - With Alum Brightness Brite BrightnessBrite (GE) Gain (GE) Gain 0 84.0 0 84.0 0 3 87.4 3.4 6 89.0 5.0 10 89.75.7 20 85.8 1.8 89.1 5.1 40 86.4 2.3 86.2 2.1 60 86.7 2.7 82.2 1.8

TABLE 3 Series I - No Alum Series II - With Alum Brightness BriteBrightness Brite (GE) Gain (GE) Gain 0 84.0 0 84.0 8 3 87.4 3.4 6 89.05.0 10 89.7 5.7 20 85.8 0.8 89.1 5.1 40 86.4 2.3 86.2 2.1 60 86.7 2.782.2 1.8

TABLE 4 Water Bath Water Bath T-100 Reaction at 60° C. at 75° C. ChargeTime Brightness Brite Brightness Brite (lbs/ton) (Hours) (GE) Gain (GE)Gain 0 0 88.9 0 88.9 0 2 1 93.0 4.1 91.8 2.9 4 1 93.6 4.6 93.4 4.5 8 194.9 6.0 94.7 5.8 0 0 88.9 0 88.9 0 2 5 92.2 3.3 92.0 3.1 4 5 93.6 4.692.7 3.8 8 5 94.0 5.1 93.9 4.9

Example 2

From a commercial IP pulp mill in Southern US, samples of fully bleachedhardwood and softwood Kraft pulp at the exit of the bleach plant werecollected and used in high consistency OBA fixation experiments.Experimental conditions, including OBA type and pulp consistency wereidentical to those described in example 1. The as-received softwood pulpsample has a pH of 5.2 and the pH for the hardwood pulp sample was 6.7.All experiments were carried out for a duration of two hours, in 65° C.temperature bath. Prior to some of experiments on hardwood pulp, dilutehydrochloric acid solution was also added to the as-received mill pulpto lower its pH to 4.9 during the reaction with OBA. The followingresults were obtained: TABLE 5 Softwood Hardwood Hardwood T-100 at 5.2pH at 6.7 pH at 4.9 pH Charge Brightness Brite Brightness BriteBrightness Brite (lbs/ton) (GE) Gain (GE) Gain (GE) Gain 0 85.5 0 85.6 085.6 0 2.5 89.4 3.9 87.5 1.9 90.1 4.5 5.0 89.7 4.2 88.5 2.9 91.3 5.710.0 91.2 5.7 89.3 3.7 15.0 91.5 6.0 90.2 4.6 92.4 6.8

Example 3

From a commercial IP pulp mill in Europe, samples of fully bleachedsoftwood and hardwood pulps, leaving the bleach plant were collected andused in OBA fixation experiments. The pH of the filtrate of both pulpsamples was 3.0. Leucophor ANO, a disulphonate OBA product produced byClariant, was used in this example. Fixation experiments were carriedout with variable OBA charges, at 10% consistency, for two hours in 65°C. temperature bath. Observed changes in the pulp brightness as resultsof OBA fixation is as follows: TABLE 6 Leucophor Hardwood SoftwoodCharge Brightness Brite Brightness Brite (lbs/ton) (GE) Gain (GE) Gain 089.3 0 88.4 0 5 93.6 4.3 92.8 4.3 10 94.3 4.9 92.1 3.7 15 92.7 3.4 90.42.0 20 91.9 2.6 89.6 1.1 30 89.3 0 86.0 −2.5

Example 4

Samples of pulps and OBA of example 3 were used in this example.However, before mixing with OBA, dilute solution of NaOH as used toraise the pH of the pulp samples, from 3.0 to 5.7 for the case ofhardwood and to 7.0 for the case of softwood. All other conditions wereidentical to those used in example 4. Observed changes in the pulpbrightness as results of pH adjustment and OBA fixation is as follows:TABLE 7 Leucophor Hardwood Softwood Charge Brightness Brite BrightnessBrite (lbs/ton) (GE) Gain (GE) Gain 0 89.0 0 87.9 0 4 93.4 4.4 92.5 4.68 94.9 5.8 93.8 5.9 12 95.1 6.3 94.0 6.1 20 95.5 6.5 94.8 6.8 30 89.36.6 95.1 7.2

Example 5

Experiments were carried out to fix T-100 on to commercially producedfully bleached softwood and hardwood Kraft pulp samples from a NorthernUS mill. The softwood pulp has a freeness of 690 csf, brightness of 90GE and pH of 4.0. The hardwood sample has a freeness of 570 csf,brightness of 89.2 and pH of 4.0. Variable dosages of T-100 were mixedwith pulps at 10% consistency and were kept in separate and sealedplastic bags. Bags were placed in 70° C. water bath for 2 hours. Changein the brightness of individual pulp samples as a result of OBA fixationis as follows: TABLE 8 T-100 Softwood Hardwood Charge Brightness BriteBrightness Brite (lbs/ton) (GE) Gain (GE) Gain 0 90.0 0 89.2 0 2 94.44.4 92.0 2.8 4 95.2 5.2 92.7 3.5 6 95.8 5.8 93.3 4.1 8 96.3 6.3 93.8 4.610 96.6 6.6 94.2 5.0 12 97.1 7.1 94.3 5.1

Example 6

The original softwood and hardwood pulp samples of example 5, togetherwith samples which were fixed with 12 lbs/bdt of T-100, were subjectedto high shear mechanical action inside a lab PFI refiner. The extent ofpulp refining was controlled so that the freeness of the softwood pulpis reduced from 690 CSF before refining to 450 CSF after refining. Forthe hardwood pulp, the freeness drop was from 570 CSF to 330 CSF.Brightness changes, as a result of PFI refining, on original pulpsamples and samples containing OBA are as follows: TABLE 9 SoftwoodHardwood Before After Before After fixation fixation Gain fixationfixation Gain Before 90.0 96.6 6.6 89.2 94.2 5.0 refining After 88.494.7 6.3 88.4 94.0 5.6 refining Loss 1.6 1.9 0.8 0.2

Brightness loss as a result of pulp refining operation is wellrecognized in papermaking. Under refining condition used in example 6,it was 1.6 points for the original softwood and 0.8 points for theoriginal hardwood. Brightness losses were very similar for the casewhere pulps were fixed with OBA, suggesting that the created bondingbetween OBA and fiber was very strong and was not affected by themechanical shear action of the refiner. The net brightness gain,obtained from OBA fixation, remained essentially unchanged and were notaffected by the pulp refining process.

Example 7

Hand Sheet Study

Summary

The handsheet study confirmed that adding Clariant Leucophor ANO opticalbrightening agent (OBA) under high consistency treatment method gavebetter brightness than when the OBA was added at low consistency.

For a fixed dose, the new addition point resulted in a brightnessincrease of about 1.9 units of ISO brightness.

Based on this study, to reach the same ISO brightness, changing to thenew addition method would allow the OBA dosage to be decreased by 3.5pounds/ton.

These estimates are based on data at OBA dose levels between 3.3 and 10pounds/ton.

The designed experiment showed that two of the factors, OBA dose(nominally 3.3 and 10 pounds /ton) and OBA addition method (new methodvs addition to low consistency pulp) were statistically significant indetermining brightness.

Experimental

1. Pulp

Pulp used for this study was unrefined hardwood and softwood taken fromthe washer of the last bleaching stage.

2. OBA Fixation

The hardwood and softwood pulps separately with two levels of OBA, 3.3and 10 pounds/ton of OBA. The OBA used was Leucophor ANO (Clariant),which is a di-sulfonated OBA. The conditions were 10% consistency, mixedfor 2 hours at 70° C.

3. Refining

Prior to refining, the pulps were combined into a 70:30 HWD:SWD ratio.Refining was performed in the LR1, a laboratory disk refiner. Twoenergies were used, 35 kW/T and 45 kW/T. The freeness of the resultingpulps were ˜580 and ˜320 csf, respectively.

4. Sheet Making

Sheets were made on the dynamic sheet former with the followingprocedure: The pulp was diluted to 1% consistency and mixed vigorously.SMI's Albacar LO PCC was added first and allowed to mix for 1 minute.Then a predetermined and accurate amount of OBA was added and mixed for15 minutes. The sheet was then formed. After forming, the sheets werepressed to 45% solids and dried at 230° F. on the drum drier. Specialprecautions were made so that the sheets with ‘fixed’ OBA had similaramounts of OBA as the standard OBA addition sheets. In addition to thesamples pretreated with OBA and the samples prepared as describe here,where the PCC was added before the OBA, several controls were also madewhere the order of addition of the PCC and OBA was reversed (OBA first).

5. Testing

The handsheets were tested for various optical properties using theDataColor Elrepho Spectrophotometer.

6. Experimental Design

The design for this experiment included four main factors:

I) Stock consistency at which the OBA was added (10% vs. 1%)

II) Refining (35 kW/T vs. 45 kW/T)

III) Filler Level (10% vs. 20%)

IV) OBA dose (3.3 lb/T vs. 10 lb/T)

Results & Conclusions

Comparison of Handsheet Brightness for New and Traditional Fixationmethods.

Adding Clariant Leucophor ANO optical brightening agent (OBA) under thenew, high consistency treatment method gave better brightness than whenadded at low consistency to handsheets. The results are set forth in thefollowing FIGS. 1 to FIGS. 1-4 shows all the brightness data from thestudy graphed against OBA dose. There are several different classes ofsamples listed, separated by the fixation method (high and lowconsistency) and filler level (10 and 20 #/ton).

Raman Spectroscopy Study of Pulp with OBA

Raman spectroscopy was used to study pulp with OBA added using theconventional as well as new processes. FIG. 5 compares the spectrum ofOBA (Leucophur ANO) with spectra of pulp with and without OBA added. Themost intensive peak at the spectrum of the OBA at approximately 1600cm⁻¹ is visible in the spectrum of pulp with the OBA added. FIG. 6 showsspectra of pulp (expanded region from 300 to 1700 cm⁻¹) with differentlevels of OBA added in the process. The intensity of the peak at 1600cm⁻¹ increased with increased level of the OBA. When spectra of the pulpwith OBA added in the conventional and the new process were compared,there were no changes in the shape of the peaks and no addition peakswere observed (see FIG. 7). In order to determine the relative amount ofOBA retained on the fibers, the ratio of the intensity of the maximum at1600 cm⁻¹ to the intensity of the peak at 900 cm⁻¹ (cellulose peak) wascalculated for pulps with different OBA levels added in the process. Theresults are presented in the table and the FIG. 8. TABLE 10 OBA added,Process lb/ton Peak Ht ratio Conv 0 0.026 10 0.469 15 0.637 20 0.711 NewHW 0 0.034 3.3 0.238 10 0.648 New SW 0 0.071 3.3 0.371 10 0.685

The results of Raman measurements indicate that the amount of OBA in thepulp produced in the new process at 10 lb/ton in comparable to theamount of OBA in the pulp obtained in the conventional process at 15-20lb/ton loading

Inductively Coupled Plasma Spectroscopy (ICP) Study of OBA in Pulp

Samples of softwood and hardwood pulp with OBA added during theconventional and new processes were hot plate digested with hydrogenperoxide and nitric acid. A sample of OBA used in the process was driedand digested under the same conditions. The digested samples wereanalyzed for sulfur content by ICP. The results are presented in thetable below. Untreated pulp was also analyzed under the same conditionsand determined sulfur concentrations were subtracted from theconcentrations in the treated pulp in order to establish the amount ofOBA present in the pulp, which is reported on the dry weight of the OBA.OBA on fiber, OBA S from ppm added, Sulfur from OBA on (based on Processlb/ton ICP, ppm fiber, ppm S results) Conv 0  150 10  190 40 697 20  250100 1744 New HW 0  140 10  250 110 1918 New SW 0   66 10  150 84 1465OBA (oven  57600; dry) 57100

The sulfur concentrations in the pulp indicate that the amount of OBApresent in the pulp treated in the new process at 10 lb/ton OBA iscomparable to the amount of the pulp from the conventional process at 20lb/ton loading.

Extraction Studies

Approximately 1 gram of pulp was cut into small pieces and soaked inapproximately 150 ml. of water for 6 hours at 60 degrees C.

The water extracts were filtered through a 0.45 μm filter, reduced toapproximately 2 ml volume in a LABCONDO Rapidvap Nitrogen EvaporationSystem using air as the purge gas. The Evaporator was run at 24% vortexspeed at a temperature of 30° C. After evaporation to approximately 2ml. the sample was brought to 5 ml. in a volumetric flask.

A portion of the water 5 ml. extract was analyzed by high performanceliquid chromatography (HPLC).

A portion of the 5 ml. water extract was diluted 1:10 for the UV/VISanalysis.

The HPLC instrumental conditions are below:

Instrument description: Waters Alliance 2695 separation module with aWaters model 996 Photodiode Array Detector (PDA)

Mobile phase: 50% methanol 50% PIC-A buffer solution at 0.7 ml minute.PIC-A is sold by the Waters Corporation and is a reverse phase ionpairing buffer solution composed of 0.005 m tetrabutyl ammoniumphosphate buffered to a pH of 7.5.

Column: Phenomenex Luna 5 μC-8 (2) 250 mm×4.6 mm, operated at 35° C.

Detector: Waters 400 photo diode array detector (PDA) over the range of200-800 nm. The peak at 254 nm was selected for the analysis.

Run Time: 60 minutes

Injection Volume: 10 μl

The UV/VIS instrumental conditions are below:

Instrument description: Shimadzu model UV-160 operated in thephotometric mode.

Wavelength used for analysis: 350 nm.

The results are set forth in FIGS. 9-11

Numerous modifications and variations on the present invention arepossible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the accompanying claims, theinvention may be practiced otherwise than as specifically describedherein.

As used throughout, ranges are used as a short hand for describing eachand every value that is within the range, including all subrangestherein.

All of the references, as well as their cited references, cited hereinare hereby incorporated by reference with respect to relative portionsrelated to the subject matter of the present invention and all of itsembodiments.

1. A method of making pulp and/or a paper substrate, comprisingcontacting a plurality of fibers in solution with at least one opticalbrightener after the last bleaching/extraction stage
 2. The methodaccording to claim 1, wherein the contacting is performed at a point inthe pulp making or papermaking process prior to a Blend Chest/MachineChest Stages.
 3. The method according to claim 1, wherein the fibers insolution are at a consistency of greater than about 4%.
 4. The methodaccording to claim 1, wherein the fibers in solution are a consistencyof from 7 to 15%.
 5. The method according to claim 1, wherein from 1 to15 lbs/ton of OBA is contacted with the fibers.
 6. The method accordingto claim 1, wherein the pH of the solution during the contacting of theOBA with fibers is from 3.5 to 5.5.
 7. The method according to claim 1,wherein the temperature when the OBA is contacted with the fibers isfrom 60 to 80° C.
 8. The method according to claim 1, wherein the OBA iscontacted with the fibers for a duration of time of from 0.5 to 6 hours.9. The method according to claim 1, wherein the contacting is performedat a point in the pulp making or papermaking process prior to a refiningstage.
 10. The method according to claim 1, comprising contacting aplurality of fibers in solution with at least one optical brightenerafter the last bleaching/extraction stage in the absence of a retentionaid.
 11. The method according to claim 1, further comprising refiningthe fibers and OBA wherein the refining is selected from at least onemember selected from the group consisting of chemical refining,mechanical refining, thermochemical refining, thermomechanical refining,and chemithermomechanical refining.
 12. The pulp made by the methodaccording to claim
 1. 13. The pulp made by the method according to claim1, wherein the pulp is bleached chemithermomechanical pulp.
 14. The pulpmade by the method according to claim 1, wherein the pulp is fluff pulp.15. The pulp made by the method according to claim 1, wherein the pulpis papermaking pulp.
 16. The pulp or paper substrate made by the methodaccording to claim 1, wherein the pulp or paper substrate has an ISObrightness that is not less than
 90. 17. The pulp or paper substratemade by the method according to claim 1, wherein the pulp or papersubstrate has a CIE whiteness that is not less than
 130. 18. The pulp orpaper substrate made by the method according to claim 1, wherein thepulp or paper substrate has a CIE whiteness that is not less than 130and an ISO brightness that is not less than
 90. 19. The method accordingto claim 1, further comprising contacting additional OBA with the fibersat a coater.
 20. The method according to claim 1, further comprisingcontacting additional OBA with the fibers at a size press.